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Re: Polar Alignment Scope - scope alignment question


Jun 20, 2007

 


----------------------------

#33268 Jun 20, 2007

Hi,

I have a Losmandy GM-100 with the original side mount polar scope.

The polar scope was not all that well aligned. Between the readout on

my Argo Navis DSC computer and some first attempts at drift

alignment, I confirmed that it points me too far south of the NCP.

The off set to the South is more then half of a degree and about 18'

West of the NCP.



The other day I unscrewed the rear optical element from the PAS and

discovered that the glass reticle is adjustable via 3 small screws. I

unscrewed the reticle retaining ring and found the glass etched

element centered in the PAS bore.



Last night I set up my mount and completed a drift alignment. The PAS

markings did not line up near the 3 stars so I removed the rear

optical elements, unscrewed the retaining ring a bit, and

repositioned the reticle using the 3 small set screws. While I was

not able to get the reticle markings to line up perfectly, it is now

very close to the three stars. The reason that I could not get the

alignment marks perfectly correlated to the 3 stars is that I pushed

the glass reticle in the bore so that I ran out of adjustment room.

It will not move any more off center.



So my question is: am I doing the right thing to improve the accuracy

of my PAS?



What I do not know is: should the reticle be perfectly centered in

the bore, and the PAS scope itself aligned to the NCP?

I am concerned that now that the glass reticle is off center in the

scope bore, the PAS will only be aligned for one night a year, last

night. I am concerned that as the PAS rotates to adjust for the time

of alignment it will be out of whack because of the reticle offset.



I have adjusted the reticle to compensate for procession. I also

understand that the PAS will not make a perfect alignment, but I

would like to get it as close as possible.



If you have any experience with the PAS, I would greatly appreciate

your input.



Clear skies,

Paul



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#33271 Jun 21, 2007

Paul



Rather than aligning the reticle to the stars, the normal way of

adjusting the reticle is to align the centre point to a fixed point.



The fixed point can either be a distant daytime object, or Polaris.



If using Polaris you align the mount so the centre cross is on

Polaris, rather than it's normal position on the line.



You then rotate the mount in RA. If the PAS is OK, then teh cross

will remain on the star. If not then adjust the screws.



Before adjusting the the PAS, check that the PAS is locating

correctly in the mount. Have a look at my web page where I show what

to check and how to fix the seating of the PAS.



www.aozc64.dsl.pipex.com/tips/g11gemini.htm#polar_scope_binding



Regards

Mark



----------------------------

#33338 Jun 24, 2007

Mark,

Thank you for the follow up. You confirmed my suspicions, my approach

was not correct.



I am going to order the new reticle as mine is from the early 90s,

then align it in the scope so the intersecting lines stay centered.

Next, I will adjust the mounting plate on the side of the GM-100 so

the finder aligns with the 3 stars. I think this will do the trick.



Thanks again!



Sincerely,

Paul





--- In Losmandy_users@yahoogroups.com, "Mark Crossley"

mark.crossley@...> wrote: >

> Paul

>

> Rather than aligning the reticle to the stars, the normal way of

> adjusting the reticle is to align the centre point to a fixed point.

>

> The fixed point can either be a distant daytime object, or Polaris.

>

> If using Polaris you align the mount so the centre cross is on

> Polaris, rather than it's normal position on the line.

>

> You then rotate the mount in RA. If the PAS is OK, then teh cross

> will remain on the star. If not then adjust the screws.

>

> Before adjusting the the PAS, check that the PAS is locating

> correctly in the mount. Have a look at my web page where I show

what > to check and how to fix the seating of the PAS.

>

>

www.aozc64.dsl.pipex.com/tips/g11gemini.htm#polar_scope_binding >

> Regards

> Mark

>



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